LAS VEGAS — Investigators say that a retired accountant's shooting rampage was meticulously planned and included specially modified weapons and surveillance cameras aimed to spy on any police intruders who would try and stop his murderous deluge.

At a late-night press conference Tuesday, authorities said Stephen Paddock made his attack even more deadly by adding more lethal components to his weapons. He had devices attached to 12 semiautomatic rifles that allowed them to mimic fully automatic gunfire.

Bureau of Alcohol, Tobacco and Firearms Special Agent in Charge Jill Schneider said Paddock had nearly 50 guns — a combination of rifles, shotguns and pistols — in three locations.

The gun attachment that mimics automatic gunfire is a little-known device called a “bump stock” that is not widely sold. The stocks have been around for less than a decade, and Schneider said officials determined they were legal.

Paddock, who killed 58 people and eventually himself, also injured 527 others in what is the deadliest mass shooting in modern U.S. history.

He also used surveillance cameras to monitor police approaches to his room at the Mandalay Bay high-rise — including a camera he positioned in the peephole of the door.

“I anticipate he was looking for anybody coming to take him into custody,” Sheriff Joseph Lombardo said.

During the Sunday night rampage, a hotel security guard who approached the room was shot through the door and wounded in the leg.

“The fact that he had the type of weaponry and amount of weaponry in that room, it was preplanned extensively,” the sheriff said, “and I’m pretty sure he evaluated everything that he did and his actions, which is troublesome.”

While Paddock's motive remains unclear, authorities were putting together a more complete picture of his work history and his past. The killer worked as a letter carrier for the U.S. Postal Service, an IRS agent and in an auditing department over a 10-year period.

A spokeswoman for the Office of Personnel Management told The Associated Press on Tuesday that Stephen Paddock’s employment included about two years as a mail carrier from 1976 to 1978.

After that, he worked as an agent for the Internal Revenue Service for six years until 1984. And then he worked a defense auditing job for about 18 months.

He graduated from college in 1977 from Cal State Northridge and also worked for a defense contractor in the late 1980s.

President Trump, as he left Washington for a trip to storm-ravaged Puerto Rico, briefly referenced Paddock, whose carnage Sunday night left 59 people dead and more than 500 injured.

"He was a sick man, a demented man with a lot of problems, I guess, and we are looking into him very, very seriously," Trump said. "We are dealing with a very, very sick individual."

The president also said the administration would be "talking about gun laws as time goes by," and he lauded the efforts of Las Vegas law enforcement.

"How quickly the police department was able to get in (to Paddock's hotel room) was very much a miracle," he said. "They've done an amazing job."

Country music star Jason Aldean was performing when Paddock opened fire from the window of his 32nd-floor hotel room overlooking the Route 91 Harvest music festival. Aldean, who was not injured, tweeted a statement Tuesday saying he has been overwhelmed with emotion since the attack.

"Something has changed in this country and in this world lately that is scary to see," Aldean wrote. But he also added that it is "time to come together and stop the hate."

Stories of heroism continued to emerge. One minute Marine veteran Taylor Winston was dancing the two-step at the concert, the next he was commandeering a pickup and shuttling the wounded to hospitals before ambulances arrived. Dawn-Marie Gray, a concertgoer who happened to have seven years experience as a paramedic, found herself providing CPR and tying tourniquets.

When Nick Jones, 30, of Vancouver, Wash., heard about the shooting, he drove 20 hours to help. He offered to donate blood, but the need had been met. He offered to volunteer at hospitals, but they had plenty of help. Even the family assistance center was overwhelmed with volunteers.

“I was worried that no one would do anything,” Jones said Tuesday. “I was happy to be proven wrong.”

Assistant Sheriff Todd Fasulo pleaded for patience during the investigation, saying authorities were "hunting down" every clue to learn more about Paddock.

Several minutes after the carnage began, officers who blasted into the room found Paddock's body. His brother Eric, who lives in Florida, says his multimillionaire brother was a big spender at casinos and often received free meals and rooms there. Eric Paddock also said he believed his brother owned a couple guns.

Police found 23 guns, including semiautomatic rifles, in Paddock's room at the Mandalay Bay Resort and Casino. They found 19 more at his home in Mesquite, Nev., 80 miles northeast of here. And in yet another home owned by Paddock in Reno, authorities found five handguns, two shotguns, and a plethora of ammunition.

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Las Vegas Metro Police have released footage from the body cameras worn by officers responding to the scene of the shooting Oct. 2, 2017.
Las Vegas Metropolitan Police Department

A federal law enforcement official, who was briefed on the matter but not authorized to comment publicly, said police also found two tripods positioned at the hotel windows in what appeared to be a fully equipped sniper’s nest.

While the investigation intensified, authorities touted the city’s resilience in the aftermath of the tragedy. Fully stocked blood banks were soon turning away would-be donors. A GoFundMe page collected $3.3 million from almost 50,000 donors in little more than 24 hours. Overall, donations for the victims have exceeded $3.7 million, Commissioner Stephen F. Sisolak said Tuesday afternoon.

Pieces of normalcy slowly returned to the iconic Strip. Club promoters hawked 2-for-1 deals, tourists took selfies and police cracked down would-be criminals.

“Do you know how disrespectful it is to come out here and deal drugs the day after 50 people died one block away?’’ a bike cop snapped at a man in handcuffs Monday night. “Can’t you take one day off?’’

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A family grieves during a candlelight vigil for Charleston Hartfield at Police Memorial Park. Hartfield, an off-duty Las Vegas police officer, was killed Sunday during the mass shooting at a music festival across from the Mandalay Bay Resort and Casino.
Robert Hanashiro, USA TODAY

Sherri Camperchioli and Jordan Cassel, volunteers from Las Vegas, staple photos of the mass shooting victims on crosses artist Greg Zanis of Aurora, Ill., constructed. He drove across the country to install them on Las Vegas Boulevard to honor the people killed in the mass shooting. Zanis said he has created crosses for many national tragedies.
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Jean Green Dunbar of Las Vegas plants shrubs at the Las Vegas Community Healing Garden in the Arts District of Las Vegas Oct. 5. The garden is intended to help the city heal from the massacre that happened Sunday.
Tom Tingle, The Arizona Republic via the USA TODAY Network

Jeanne Belez of Marysville, Ore. places a bouquet of flowers at a memorial on a median on Las Vegas Blvd. near the Mandalay Bay Hotel and Casino in Las Vegas on Oct. 4, 2017.
Robert Hanashiro, USA TODAY

Arizona Diamondbacks remember their former employee Christiana Duarte, who was killed this week in the Las Vegas shooting during pregame ceremonies of the National League Wild Card game on Oct. 4, 2017 in Phoenix, Ariz.
Rob Schumacher, The Arizona Republic, via USA TODAY NETWORK

Crystal Fernandez, left, and Carmen Arias share a moment at a memorial that sprung up on a median on Las Vegas Blvd. near the Mandalay Bay Hotel and Casino in Las Vegas on Oct. 4, 2017.
Robert Hanashiro, USA TODAY

Linda Proctor hugs Dr. Robert T. Baggott as her husband, Donnie Proctor, waits to the right during a memorial at Community Church of Vero Beach, Fla. on Oct. 4, 2017, for those who died in the mass shooting in Las Vegas.
Jeremiah Wilson, TCPalm, via USA TODAY NETWORK

President Donald J. Trump and First Lady Melania arrive at McCarran International Airport in Las Vegas. . President Trump is planning on meeting victims of Sunday's mass shooting.
Robert Hanashiro, USA TODAY

With the lights of the Las Vegas Strip as a backdrop, people gathered on a vacant lot on Las Vegas Blvd. for a candlelight vigil in the memory of the victims of the Mandalay Bay mass shooting, Oct. 2, 2017.
Robert Hanashiro, USA TODAY

Michael Kordich, 34, a firefighter with the San Bernardino County Fire Dept., performed CPR on a fellow concert goer who had been shot, before Kordich himself was shot in the arm during the Las Vegas massacre. He talks about the life-changing events from his hospital bed at Sunrise Hospital and Medical Center, Oct. 3, 2017.
Tom Tingle, The Arizona Republic via the USA TODAY Network

Sara Rivero, on right, with her mom Laura Rodriguez, in center and Gisell Rivera, her step mother, burn a candle at the memorial site on Las Vegas Blvd, for friends who died at the concert.
Nick Oza, The Arizona Republic via the USA TODAY Network

Members of the Las Vegas community pray during an emotional vigil for the victims of the Las Vegas shooting at Mountain Crest Park, Oct. 3, 2017.
Jay Calderon, The Desert Sun Via the USA TODAY Nertwork

Matthew Edwards puts a teddy bear and flowers at the memorial site. When asked about his feelings he said "I cannot understand what has happened here... what would drive a man to do what he did"
Nick Oza, The Arizona Republic via the USA TODAY Network

With the lights of the Las Vegas Strip as a backdrop, people gathered on a vacant lot on Las Vegas Blvd. for a candlelight vigil in the memory of the victims of the Mandalay Bay mass shooting, Oct. 2, 2017.
Robert Hanashiro, USA TODAY

People gather at Trocadero plaza as the lights of the Eiffel tower are turned off, in Paris on Oct. 2, 2017. Paris mayor Anne Hidalgo said the Eiffel tower will turn off its lights to pay tribute to Las Vegas and Marseille victims.
Kamil Zihnioglu, AP

The American flag is at half-staff at the White House in Washington on Oct. 2, 2017. President Donald Trump ordered that flags be lowered at all government buildings to honor the victims of the mass shooting in Las Vegas.
Pablo Martinez Monsivais, AP

People walks past flowers left on a pedestrian bridge overlooking Las Vegas Blvd. in Las Vegas on Oct. 2, 2017, two blocks from the Mandalay Bay Hotel Casino where a gunman killed dozens and injured hundreds of people attending a concert.
Robert Hanashiro, USA TODAY

Broken windows are seen on the 32nd floor of the Mandalay Bay Resort and Casino after a lone gunman opened fired on the Route 91 Harvest country music festival on Oct. 2, 2017, in Las Vegas.
David Becker, Getty Images

An injured person is tended to in the intersection of Tropicana Ave. and Las Vegas Boulevard after a mass shooting at a country music festival nearby on October 2, 2017 in Las Vegas.
Ethan Miller, Getty Images

A woman sits on a curb at the scene of a shooting outside of a music festival along the Las Vegas Strip, Monday, Oct. 2, 2017, in Las Vegas. Multiple victims were being transported to hospitals.
John Locher, AP

People are searched by Las Vegas police at the Tropicana Las Vegas during an active shooter situation on the Las Vegas Strip. Multiple victims were being transported to hospitals after a shooting late Sunday at a music festival on the Las Vegas Strip.
Chase Stevens, Las Vegas Review-Journal via AP

A Las Vegas Metropolitan Police officer stands in the intersection of Las Vegas Boulevard and Tropicana Ave. after a mass shooting at a country music festival nearby on October 2, 2017 in Las Vegas.
Ethan Miller, Getty Images

People take cover at the Route 91 Harvest country music festival after apparent gun fire was heard on October 1, 2017 in Las Vegas, Nevada. There are reports of an active shooter around the Mandalay Bay Resort and Casino.
David Becker, Getty Images

Derek Koerner, who identified himself as a licensed club promoter, said he was encouraged by the sizable crowds — and particularly grateful for the SUV full of men interested in his 2-for-1 deals on strip clubs. A $40 cover for a two-drink minimum gets the buyer into the second strip club for free.

“There’s more people out here than I thought there’d be,’’ said Koerner, 48. “People seem to be upbeat and have a good energy. People seem to be moving on with their lives.’’

But less than a mile away, the mood was noticeably different. Dozens of people, some arriving with candles and flowers, returned to the scene of the horrific crime, marked by yellow police tape.

Herman Gold and his ex-wife, Sara, stood near the concert grounds and explained how they escaped the hail of bullets and why they came back.

“I just want closure,’’ Herman Gold said. “Why? What’s the reason that on that particular night, one individual would sacrifice everyone else for his insanity?’’

Joe Larsen, standing at the same corner and wearing a VIP wristband from the Aldean concert, expressed gratitude.

Larsen, 49, who flew in from New Jersey for the concert, said that he watched the Twin Towers fall in 2001, lost his wife to cancer in 2015 and, on Sunday night, feared he was about to leave his son and daughter without a parent.

He said he saw a young woman die from a bullet to the head before he called his father during the bedlam.

“I told him, ‘I don’t know if going to make it. Tell my kids to live a good life’ ” Larsen recalled.

As he and others shared their stories and wiped away tears, police officers closely monitored pedestrians, especially the wayward ones.

“Sir, get out of the street,’’ one officer barked. “It’s the last time I’m telling you.’’

Investigators have still not discovered what motivated Stephen Paddock to embark on the worst mass shooting in modern U.S. history, but determined that he researched SWAT tactics ahead of the massacre and investigated other possible targets. (Jan. 19)
AP

SportsPulse: USA TODAY Sports NHL reporter Kevin Allen believes Las Vegas and its new hockey team have already formed a special bond and culture that could make it a flagship franchise.
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Erick Silva was helping concert goers escape when he was shot and killed. A co-worker who witnessed it moved Silva’s body away from a stampeding crowd. After being shot himself, he found Silva’s mother in order to explain her son’s final moments. (Oct. 8)
AP

Nevada officials said Sunday that seven truckloads of personal belongings had been collected from the scene of the mass shooting in Las Vegas. Among the items were purses, cell phones and clothing they were hoping to return to concert-goers. (Oct. 8)
AP

Vice President Mike Pence says in the depths of horror, Americans have found hope in those who risked their lives after the Las Vegas shooting. He made the remarks at a Las Vegas prayer service. (Oct. 7)
AP

Following a ceremony in Las Vegas where U.S. Vice President Mike Pence joined residents in marking last weekend's massacre at a country music concert, doves were released outside City Hall. (Oct. 7)
AP

Las Vegas Police say they still do not have determined a motive for gunman Stephen Paddock, who killed 58 fans gathered at an outdoor concert and injuring 500 more before killing himself on Sunday evening at an outdoor concert in Las Vegas. (Oct. 6)
AP

First responders detailed Thursday the chaos that followed the mass shooting in Las Vegas Sunday night. Clark County Fire Chief Greg Cassell credits emergency response crews with being on scene within five seconds of the attack. (Oct. 5)
AP

Clark County Coroner John Fudenberg said all 58 victims in the shooting at a Las Vegas concert have been identified and families notified. Fudenberg declined to answer questions about how the victims died. (Oct. 5)
AP

Survivor of the mass shooting at Las Vegas, Heather Melton, of Tennessee, is crediting her husband for her survival. Her 29-year-old husband, Sonny, ultimately died of his injuries after shielding his wife from the barrage of bullets. (Oct. 4)
AP

A Las Vegas shooter’s perch in a 32nd-floor hotel room overlooking 22,000 people jammed into a country music festival below is just the kind of nightmare scenario police dread in places where big crowds and high-rises mix. (Oct. 4)
AP

Las Vegas Sheriff Joseph Lombardo said the alleged Las Vegas gunman had cameras, and he was likely monitoring his surroundings. Lombardo said, "I anticipate he was looking for anybody coming to take him into custody."
USA TODAY

A retired police sergeant from California says he drove to Las Vegas to help as soon as he found out one of his former colleagues, Rachael Parker, had been killed in the Mandalay Bay Resort shooting on Sunday. He called Parker a "great person." (Oct. 3)
AP

Amateur video footage has emerged showing Stephen Paddock's room at the Mandalay Bay Hotel in Las Vegas where he fired on concert-goers Sunday evening, killing 59 people. It was recorded by a hotel visitor who stayed in the room in 2016. (Oct. 3)
AP

LAS VEGAS STRIP SHOOTING, AT LEAST 50 DEAD
Gunman had 23 firearms at hotel, 19 more at home | 1:01

Police say the gunman in the Las Vegas Strip shooting had 23 firearms in his hotel room and an additional 19 at one of his two homes. Police say they're searching for a motive for the shooting. (Oct. 3)
AP

More dramatic cell phone video has emerged of the terrifying moment a gunman fired a hail of bullets on an outdoor country music festival on the Las Vegas Strip, killing at least 58 people and injuring more than 500. (Oct 2.)
AP

A motion graphic explaining how the events unfolded when Stephen Paddock opened fire from his hotel room on concert goers at the Route 91 Harvest music festival near the Mandalay Bay resort and casino on the Las Vegas Strip.
Ramon Padilla, Janet Loehrke George Petras, Jim Sergent USA TODAY

The brother of the suspected Las Vegas shooter, Stephen Paddock, says he's in total disbelief. Eric Paddock says he last talked to his brother months ago via text and saw no warning signs that he would commit mass violence.
USA TODAY

A concertgoer captured the moment a gunman opened fire on an outdoor music festival on the Las Vegas Strip, killing scores of people and wounding hundreds of others. Country music star Jason Aldean was performing when the gunfire began.
AP

Investigators believe Stephen Paddock checked into the Mandalay Bay Resort and Casino days before the worst mass shooting in modern U.S. history. Here's what we know about the suspected gunman.
USA TODAY

Las Vegas Metropolitan Police say one of their own was among the scores of concertgoers killed when "lone wolf" gunman Stephen Paddock opened fire on crowds at the Route 91 Harvest music festival.
USA TODAY

Video shows Jason Aldean realizing there was a barrage of bullets being fired during his concert in Las Vegas. Katherine Van Buren, who was recording the Facebook Live, said strangers took her into their hotel room after they escaped the shooting.
USA TODAY